According to http://maryjaneshoes.org.uk/:
“Mary Jane shoes are essentially strapped shoes (or sandals) that have a few distinct features. Firstly, Mary Jane shoes (Wiki) are almost always low heeled although there are some exceptions. Secondly, the toes on the shoe are always rounded and they are always closed. Lastly, Mary Jane shoes feature a strap near the ankle.”
Having had a root around in the bottom of the cupboard, I found some shoes that were as close to the definition as I could find. These don’t have low heels (I don’t really do low), they almost have round toes, but they definitely have ankle straps!
One of my team in my day job has over 60 pairs of shoes. In fact, she has so many, that she stores some with other members of her family as her own cupboard is just not big enough. She only has one pair of flat shoes and is particularly partial to a Kurt Geiger 🙂